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Home , Acutiramus, Eurypterid, Hughmilleria, Metastoma, Overath, Pterygotidae

Mitt. Mus. Nat.kd. Berl., Geowiss. Reihe 5 (2002) 93-104 10.11.2002

The Early Grossopterus overathi (Gross, 1933) from Overath,

Jason A. Dunlopl, Simon J. Braddy2 & Erik Tetlie2

With 6 figures

Abstract

The and only known specimen of the eurypterid (: Eurypterida) Grossopterus overathi (Gross, 1933) from the Early Devonian (Siegennian) of Overath, north-west Germany is redescribed. Based on comparisons with other eurypterid taxa we interpret G. overathi as having a well-preserved type B genital appendage, which exhibits two apomorphic character states: (1) a furca fused into a single, spatulate plate and (2) marginal serrations near the distal end of the appendage. Grossop- terus is assigned to the family Hughmilleriidae, but its resembles that of the larger Slimoniu acuminatu (Salter, 1856) (Slimoniidae). A provisional phylogenetic analysis resolves Grossopterus as the sister group of (Slimonia + Pterygotoidea). The large pterygotids, in particular, have been suggested as significant predators on early vertebrates and hypotheses about eurypterid-fish co-evolution are reviewed, in particular Romer’s proposal that dermal annour in fish evolved in response to eurypterid .

Key words: Devonian, north-west Germany, Overath, Eurypterida, Grossopterus, Genital appendage, fish, co-evolution.

Zusammenfassung

Der Holotyp - das einzig bekannte Exemplar - des Eurypteriden (Chelicerata: Eurypterida) Grossopterus overathi (Gross, 1933) aus dem friihen Devon (Siegennian) von Overath im nordwestlichen Deutschland wird wieder beschrieben. Basierend auf Vergleichen mit anderen Eurypteriden-Taxa interpretieren wir G. overathi als Trager eines Typ B-Anhanges, wobei zwei apomorphe Merkmalszustande vorliegen: (1) die Furca ist zu einer einzigen, spatelformigen Platte verschmolzen, und (2) der Seitenrand nahe des distalen Endes des Genitalanhanges ist gezahnt. Grossopterus wird zur Familie der Hughmilleriidae gestellt, aber der prosomale Dorsalschild ahnelt der groljeren Slimoniu acuminata (Salter, 1856) (Slimoniidae). Eine vorlaufi- ge phylogenetische Analyse zeigt Grossopterus als Schwesteruppe von (Slimonia + Pterygotoidea) auf. Besonders die groljen Pterygotiden wurden als signifikante Pradatoren von friihen Vertebraten gehandelt, und Hypothesen zur Eurypteriden-Fisch Koevolution werden iiberpriift, speziell Romers Vorschlag, dass die dermale Panzerung von Fischen als Antwort auf die Pradation durch Eurypteriden evolvierte.

Schliisselworter: Devon, Nordwestdeutschland, Overath, Eurypterida, Grossopterus, Genitalanhang, Fische, Co-Evolution.

Introduction eurypterid material. Stormer (1934) redescribed E. (?) overathi in some detail and established a In 1933 Walter Gross described a fauna of fish new genus for it, Grossopterus Stormer, 1934, and collected by himself and Walter which he named after Gross and diagnosed on Schriel from Early Devonian sediments at a characters such as the carapace shape with in- quarry in Overath, near , Germany. curving lateral margins and the shape of the Among the fossils figured by Gross (1933) were genital appendage (see also below). In the same fragments of pterygotid eurypterids and an al- paper an incomplete specimen from the Middle most complete specimen which he named Eur- Devonian of the USA, inexpectans ypterus (?) overathi Gross, 1933. Subsequently, Ruedemann, 1921 was tentatively referred to W. Gross invited Leif Stcwmer to re-examine this this new genus. G. overathi was also figured in

Museum fir Naturkunde, Institut fir Systematische Zoologie, InvalidenstraBe 43, D-10115 Berlin, Germany. E-mail: [email protected] Department of Earth Sciences, University of Bristol, Wills Memorial Building, Queens Road, Bristol, BS8 lRJ, UK. E-mail: [email protected] [email protected] Received February 2002, accepted May 2002

0 2002 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim 1435-1943/02/0511-0093 $17.50+.50/0 94 Dunlop, J. et al., Redescription of Grossopterus the Treatise on Invertebrate Paleontology (Stgr- overathi could, therefore, be a member of mer 1955). the lineage which led to some of the largest eur- Work on eurypterid systematics was domi- ypterids; up to two metres long nated in the mid- 20th century by Leif Stgrmer, which are popularly perceived as having been Erik Kjellesvig-Waering and Charles Waterston. significant predators on early vertebrates. As at However, since the late 1970s most publications Overath, Siluro-Devonian eurypterids are often on eurypterids have been palaeobiological, to- found in association with fish, leading Romer gether with the descriptions of a few new taxa. (1933) to speculate that eurypterids exerted a se- With the exception of Tollerton’s (1989) valuable lective pressure for the development of verte- compilation of genera and suprageneric taxa, brate dermal armour. This hypothesis is dis- there have been few recent systematic revisions. cussed below in the light of recent critical Tollerton (1989, table 8) recognised over sixty remarks. valid eurypterid genera (excluding the unusual cyrtoctenids), at least seven of which could not be placed within his familial scheme because Material they were based on incomplete, or even frag- mentary, material. Indeed, eurypterid systematics Both Gross (1933) and Stormer (1934) cited the type reposi- tory of G. overathi as the Geologisches Landesmuseum Ber- is plagued by taxa raised on isolated head lin. The Landesmuseum material now forms the palaeontolo- shields (Ruedemann 1921), (Kjellesvig- gical collection of the Museum fur Naturkunde, Berlin (MfN) Waering 1951, 1973) or the dentition of disarticu- and the holotype, and only specimen, of G. overathi is held here in the palaeontology collections under the lated (Kjellesvig-Waering 1964), and repository number MB.A. 2a+b (i.e. part and counterpart). on names assigned to non-descript stains and The holotype of G. overathi was examined under a stereomi- other non-eurypterid material; see e.g. Toller- croscope with a camera lucida attachment used to draw the genital region in detail. Specimens were compared to other ton’s (1994) comments on many of the Ordovi- eurypterid taxa, principally Battoeurypterus Stprrmer, 1973, cian taxa from State. Erettopterus Salter, 1859, Sfimonia Page, 1856 and Hughmil- Tollerton’s (1989) typological scheme of higher leria Sarle, 1903, based on the literature and material in var- ious collections including the MfN, the Natural History Mu- systematics has not been translated into a parsi- seum, London, the National Museum of , Edinburgh mony-based model of eurypterid evolution. The and the Sedgwick Museum, Cambridge. Tenninology follows only comprehensive cladistic analyses are in the Stprnner (1955) and Tollerton (1989) and also Selden (1981) for the appendages and Braddy & Dunlop (1997) for the unpublished theses of Plotnick (1983) and Brad- genitalia. dy (1996); a version of Plotnick’s cladogram was figured by Beall & Labandeira (1990), but with- out accompanying discussion. There is also a Geological Setting published analysis of the pterygotid genera by Plotnick & Baumiller (1988). Redescriptions of Schriel (1933) described the stratigraphic and some of the less well known or taxonomically tectonic setting of the Overath fossils. The fish complex genera are an important prerequisite and eurypterids, including G. overathi, were col- for scoring characters into future phylogenetic lected from a 10-20cm thick unit (Gross 1933) studies; see also comments in Braddy (2000). in the Heider quarry which belongs to the In this paper we redecribe G. overathi as part Wahnbach-Schichten of the Rheinische Schiefer- of a wider systematic revision of the Eurypteri- gebirge and was noted by Schriel as the most da. In contrast to StQrmer (1934), we reinterpret important locality for dating this Early Devonian its genital appendage as a type B appendage, but formation in the Overath region. According to one in which the distal furca has fused into a both Schriel (1933) and more recently Schweit- spatulate plate with marginal serrations. This di- zer (1983: table 4) the Wahnbach-Schichten is agnostic character appears to be autapomorphic mid- to late Siegennian in age; a date also given for the genus. Grossopterus shares potential on the G. overathi labels. The associated fish fau- characters with members of the Hughmilleriidae, na from the Heider quarry includes agnathans, to which it was originally assigned (Stormer elasmobranchs and crossopterygians. A large 1955, Tollerton 1989), but also with the larger amount of (mostly unidentified) plant material Slirnonia acurninatu (Salter, 1856) (Slimoniidae). was also reported (see Gross 1933 for details). Here, we present a preliminary phylogenetic analysis based on selected taxa, the results of which imply that G. overathi, S. acurninata and the pterygotid eurypterids may form a clade. G. Mitt. Mus. Nat.kd. Berl., Geowiss. Reihe 5 (2002) 95

Fig. 1. Grossopterus overathi (Gross, 1933). MB.A. 2a + b. From the Early Devonian (Siegennian) Wahnbach-Schichten, col- lected at the Heider quarry near Overath, Nordrhein-Westfalen, Germany. A. Dorsal surface showing prosomal dorsal shield (or carapace), most of the and some appendages. B. Ventral surface showing the , some coxal ele- ments and an incomplete opisthosoma with a prominent genital appendage. Scale bar equals 20 mm.

Morphological interpretation The part has a split through the middle of the and both halves are mounted together in G e n e r a 1: Grossopterus is preserved in a dark a plaster of Paris jacket. Grossopterus is a small grey shale with relatively little visible lamination to medium-sized eurypterid with a body length (Fig. 1).The matrix around the part, showing the of about 20 cm excluding the (absent) . It dorsal surface, is coloured bluish-grey which con- appears slightly larger and more robust than the trasts against the dark brown specimen. This otherwise similar genus ; especially blue colouration is not seen on the counterpart. with respect to the prosomal appendages. Gros- 96 Dunlop, J. et al., Redescription of Grossopterus

Fig. 2. Interpretative drawings of the specimens shown in Fig. 1. A. Dorsal view. B. Ventral view. Opisthosomal segments numbered (1-11) conventionally after St0rmer (1955). Segment 12 not preserved. bs, basal appendage podomeres?; ep, epi- mera; fi, flanges on coxa VI; fo, folds near incurving anterior margin; ga, genital appendage; gn, gnathobase on coxa VI; le, reniform lateral eye tubercle; mb, possible membrane from between the dorsal and ventral surfaces; mt, metastoma; oc, prob- able site of ocelli or median eyes; or, ornament; pd, paddle (leg VI); ps, prosomal dorsal shield or carapace. Scale bar equals 20 mm.

sopterus overathi is relatively complete (Figs 1, Prosoma : The prosomal dorsal shield, or cara- 2), the dorsal side more so than the ventral one, pace, is subrectangular, slightly wider than long and the postabdomen has bent slightly to the and has a more or less straight posterior margin left. The exhibits some folding and wrink- (Fig. 1A). As Stgrmer (1934) noted, the right ling; presumably taphonomic in origin. Under margin of the carapace curves inwards; a similar higher magnification the typical eurypterid cuti- morphology to that seen in the much larger Sli- cle ornament of lunules can be seen, especially monia. The precise of this curvature was on the ventral surface near the genital appen- better expressed in Gross’s drawings as com- dage (Fig. 3). pared to Stgrmer’s and it is worth noting that Mitt. Mus. Nat.kd. Berl., Geowiss. Reihe 5 (2002) 97

Fig. 3. Camera lucida drawing of the genital appendage in G. overathi and its associated operculum (2) plus the following operculum (3). go, genital operculum; ms, median suture line; pj, proximal joint of genital appendage, se, serration on appen- dage margin, sp, spatulate distal region of genital appendage, ts, transverse suture across genital operculum. Scale bar equals 10 mm. the whole animal has been inverted in the Trea- the terminal one formed into a curving spine. tise illustration (Stormer 1955: fig. 21(4a)). There The other podomeres all have short, thick spines is also a shallow incurving of the anterior margin emerging from the distal, inferior margin and in in G. overathi close to the midline, associated the scheme of Tollerton (1989: fig. 8) this would with what appear to be a series of folds. The lat- match the Hughmilteria-type of spiniferous limb. eral eye tubercle is preserved only on the right The remaining appendage is clearly number VI, side where it occupies an anterolateral position. being modified into a swimming paddle. It is, It is reniform in shape and lies close to, but does however, rather small when compared to the not touch, the margin of the dorsal shield. The paddles of similar taxa. At least three podo- median eyes, or ocelli, are not clearly preserved, meres are visible, but it is difficult to resolve pre- but a region on the midline, just into the poster- cise homologies for these limb elements and, in ior half of the dorsal shield (Fig. 2A), is consis- comparison to better preserved eurypterids, de- tent with being the median eye tubercle. tails of the structure of the paddle unit are ob- Four individual appendages can be seen in the scure. In particular, podomere 7a cannot be part. The distal region of a small, spinose appen- clearly seen and the entire paddle probably lies dage (possibly appendage 11) emerges from be- upside down, since it is preserved curving away neath the front of the dorsal shield. Two larger from the body while in most eurypterids the pad- appendages (probably IV and V) are preserved dle follows the curvature of the preabdomen. on the right side. Both are robust and the poster- On the counterpart the ventral prosomal re- ior one is especially well preserved, lying on its gion is poorly preserved (Figs lB, 2B). On the lateral side to reveal five podomeres, including left side it is possible to identify the enlarged 98 Dunlop, J. et al., Redescription of Grossopterus coxa of limb VI. It has become displaced from for a review). Since this question its life position but the medial gnathobasic edge remains unresolved, the conventional scheme of can still be identified (Fig. 2~:gn), albeit without numbering eurypterid segments sensu StGrmer the teeth of the gnathobase being preserved. (1955) is adopted here. The posterior margins of This structure also has two distinct flanges: a me- tergites 2-5 have an ornament of raised, V- sal flange which in life would tuck under the me- shaped scales. A region on the right side of the tastoma (see below) and an anterior flange (cf. preabdomen appears to be slightly separated Parahughmilleria hefteri Stmner, 1973) of uncer- from the rest of the specimen with fold-like tain function. In front of the genital appendage markings running more or less longitudinally. is the metastoma. This plate-like structure This may be the impression of the membrane (Fig. 2B) was not recognised by Stflrmer (1934) between the tergites and sternites squeezed out and is poorly preserved, but in outline it is laterally during compression, rather than part of bluntly rounded posteriorly and widens ante- the tergites themselves. The postabdominal seg- riorly forming a pair of curving shoulders giving ments show traces of small, lateral epimera on it a more or less cardioid shape (cf. Tollerton the posterior margin. Ventrally the posterior 1989: figs4-5). On the right side is an isolated margins of segments 8 and 9 have an ornament limb, probably limb I1 or I11 judging by its posi- of narrow, wedge-like structures. The pretelson tion and small size compared to the large, spi- (segment 12) and telson are not preserved. The nous limb on the part. Superimposing the two structure of the genital appendage, and its asso- camera lucida drawings suggests that this limb in ciated operculum (Fig. 3), is considered below. the counterpart is not the small limb projecting from beneath the front of the carapace in the part. Posterior to this limb are three elements Genital appendage which could be part of the basal region of the legs, probably composed of two or more indis- Eurypterid genitalia are known in greatest detail tinctly preserved podomeres. from the genus Baltoeurypterus; see e.g. 0 pi s t h o s o m a : The opisthosoma of Grossop- Wills (1965) and Braddy & Dunlop (1997). Most terus has a fairly smooth transition between the well-preserved eurypterids exhibit sexual di- pre- and postabdomen. Twelve opisthosomal seg- morphism (Figs 4-5) with so-called type A and ments are traditionally recognised in eurypterids type B genital appendages; although in taxa - seven in the preabdomen, five in the postab- where ontogenetic series are preserved there can domen - although there is some evidence for a be variability even within one of these appen- vestigial segment between the carapace and the dage morphologies (Waterston 1960, 1964). In first visible tergite (see Dunlop & Webster 1999 Baltoeurypterus there is a fairly straightforward

Fig. 4. Comparison of genital appendages in selected euryp- tend taxa. A. Baltoeurypterus tetragonophthalmus - type A appendage. B. 3. tetrugo- nophthalmus - type B appen- dage. Both after Braddy & Dunlop (1997: fig. 2). C. Gros- sopterus overathi (this study). D. Nanahughrnilleria norvegica - type A appendage (?), after Starmer (1934: pl. 1). E. H. so- cialis - type B appendage (?), after Clarke & Ruedemann (1912: pls 59, 62). The Grossop- terus appendage is similar to that of H. socialis, at least in the proximal region. Grossop- terus has only two segments which suggests that it is a type B (?male) appendage, while the spatulate distal region might re- present the fusion of the two elements forming the distal fur- ca in other eurypterids. Draw- ings not to scale. Mitt. Mus. Nat.kd. Berl., Geowiss. Reihe 5 (2002) 99 division. The type A genital appendage (Fig. 4~)joint (Fig. 5~)while in pterygotids the entire consists of three sections (proximal joint and dis- structure forms an ovoid or triangular plate tal joint plus a pair of tapering projections called (Fig. 5~). the furca) and the proximal joint is large and is noticeably longer than the surrounding plate, the G r o s s opt e r u s : The genital appendage of G. genital operculum. Braddy & Dunlop (1997) re- overathi was described by Stgrmer (1934: fig. 3) viewed previous attempts to assign the different in some detail and based on its overall length he morphologies to either males or females, settling originally interpreted it as a type A. In this fossil on the interpretation that the type A morphol- the right side of the genital operculum, and the ogy was female since it is associated in Baltoeur- succeeding operculum, or Blattfuss, is better pre- ypterus with a pair of sclerotised, sac-like, inter- served than the left (Fig. 3). Indeed the differ- nal structures interpreted as sperm-storing ences in ornamentation between the two sides spermathecae. (lunules on the right and fine, angled lineations In contrast, in most eurypterids the type B on the left) may reflect the fact that the right genital appendage, which in this model is impli- side preserves the ventral surface of the opercu- citly male, has only two sections (proximal joint lum while the left side may be preserving struc- and furca). Here, the proximal joint is narrower tures at a different level; for example the poorly and shorter. In most taxa where this structure is known dorsal surface of the operculum. known, the type B proximal joint is about as Anteriorly, the genital operculum of G. over- long as, or barely extends beyond, the genital athi (Fig. 3) projects slightly, with the projection operculum, while in some taxa, e.g. Baltoeuryp- formed from a double hump. The proximal joint terus, it only extends about half way-down the is arrow-shaped anteriorly and on the right side genital operculum (Fig. 4~).Thus, both the num- the barb of the arrow is seen to merge with a ber of elements (two or three), together with the transverse suture running part of the way across length of the proximal joint (longer than or the genital operculum in a gentle curve and di- shortedequal to the operculum), appear to be viding the lunule ornament below it from an or- useful criteria for determining the sex of a eur- nament of fine lines above. This fine, linear orna- ypterid (Fig. 4); see also Tollerton (1989: fig. 13). ment continues across the top of the proximal These criteria are, however, less applicable to joint. The proximal joint then continues behind the apparently more derived genitalia of taxa the arrow-shaped part as a squat, slightly taper- like Slimonia and the pterygotids (see e.g. ing tube. Pairs of strong lines running along the Waterston 1960, 1964). Both groups appear to length of the proximal joint ornament the struc- show varying degrees of fusion compared to the ture in this region, the outer lines curve laterally Baltoeurypterus model. The type B appendage in towards the anterior end and merge with the Slimonia has an unusually elongate proximal transverse suture (Fig 3). This pattern of lines

Fig. 5. Further comparisons of genital appendages in selected eurypterid taxa. A. Slimonia acuminata - type A appendage. B. S. acuminata - type B ap- pendage. Both after Waterston (1960, text-figs. la, 3a). C. Hughmilleria banksii - type B appendage (?), after Kjellesvig- Waering (1951, text-fig. 1H). D. Erettopterus bilobus - type A appendage. E. E. bilobus - type B appendage. Both after Waterston (1964, text-fig. 1). Like Grossopterus, H. banksii also appears to have a fused furca. The genital appendages of Slimonia and the pterygotids are increasingly derived from the (?plesiomorphic) Baltoeur- ypterus condition. Drawings not to scale. 100 Dunlon J. et al., Redescrktion of Grossovterus creates the back of the arrowhead. The proximal Systematic palaeontology joint ends shortly before the posterior margin of the genital operculum. Tucked close behind the Order Eurypterida Burmeister, 1843 posterior end of the proximal joint, the mesial Family Hughmilleriidae Kjellesvig-Waering, 1951 region of the operculum is developed into a Genus Grossopterus Stgrmer, 1934 small, rounded lobe (Fig. 3). This feature is only Type - spe c i e s : Grossopferus overathi (Gross, 1933) preserved on the right side in G. overuthi and is Add i t i o n a 1 s p e c i e s : Grossopferus (?) inexpectans (Rue- observed quite commonly in eurypterids, where demann, 1921) it is characteristic for the genital operculum (see Rem a r k s : Grossopterus (?) inexpectuns is e.g. figures in Starmer 1955). known only from the carapace which, as Stgrmer Grossopterus overathi has no obvious distal (1934) remarked, is similar to that in G. overathi. joint in the genital appendage, and instead of the The G. (?) inexpectuns type was originally re- double-branched furca (e.g. Figs 4A-B, D-E) it ferred to the genus Pterygotus Agassiz, 1844 but has a single, spatulate plate (Figs3, 4C). The from published descriptions this isolated cara- proximal region of this plate has a distinct med- pace lacks the massive lateral eyes which are ian suture line while the posterior margins are characteristic for pterygotids. However, it shows developed into a series of tooth-like projections. few reliable diagnostic characters. We have been This serrated margin was one of Starmer’s (1934, unable to examine the type, but suspect that due 1955) diagnostic characters, and when examined to its incompleteness Ruedemann’s may in detail the serrations on the fossil are restricted have to be regarded as a . to the posterior end and the right side of the genital appendage. Care must be taken to distin- guish between genuine serrations and prepara- Grossopterus overathi (Gross, 1933) tion artefacts around the genital appendage, but Figs 1-3, 4C Starmer’s observation is confirmed in this study. This spatulate element in extends a 1933 (?)overathi Gross: 72-74, fig. 16, pl. 7, fig. 1. G. overathi 1934 Grossopterus overuthi (Gross) - Stormer: 288-291, little beyond the succeeding operculum. figs 1, 3. Since there are only two elements in the G. 1955 Grossopterus overathi (Gross) - Stormer: 30, fig. 21 (4). overuthi genital appendage and since the proxi- 1973 Grossopterus overathi (Gross) - Stormer: 121. mal element does not extend noticeably beyond Holotype and only specimen: MB.A. 2a+b; al- most complete specimen preserving dorsal and ventral sur- the operculum we suggest that it is more consis- faces. tent with the type B appendage (Fig.4). In this model MB.A. 2a + b (the holotype) is inter- D i a g n o s i s : Medium-sized eurypterids with a preted as a male. We suggest that instead of a subrectangular carapace with incurving lateral furca G. overuthi has fused this paired element margins and anterolateral eyes; lateral eyes not together into a single plate, and that the median touching the margin. Metastoma cardioid. Type suture is a relict of its paired origin. In his illus- B genital appendage distinctive, divided into trations of the British species Hughmilleriu bank- two parts. Distal part spatulate, partly divided sii (Salter, 1856), Kjellesvig-Waering (1951: text- by a median suture and uniquely with marginal figs lH, K, pl. 2, figs 4-5) showed what appears serrations. Emended from Stgrmer (1934, to be another example of a type B appendage 1955). with the furca fused together into a single struc- Ty p e - 1o c a 1it y : Steinbruch Heider [Heider ture (Fig. 5c). Furthermore, if the eurypterid quarry], near Overath, Nordrhein-Westfalen, genital appendage is homologous with the paired Germany. Holotype collected by Walter Gross in gonopods seen in - which also occur autumn, 1931. in a reduced or modified form in certain ara- Ty p e - h o r i z o n : Overather Fischschichten, chnids - then the unfused furca seen in most eurypterid taxa should probably be interpreted Wahnbach-Schichten, Early Devonian (Middle to as the plesiomorphic condition of the clade. Fu- Upper Siegennian). sion of the furca into a single plate would, in this D e s c r i p ti o n : Total preserved length 194 111111. model, be an apomorphic feature within euryp- Carapace subrectangular, wider than long; length terids, while the presence of a serrate margin is 45mm, maximum preserved width 55mm. Lat- an autapomorphy which defines the genus Gros- eral margin of carapace with distinctly incurving sopterus. margin, narrowest about two thirds along its length. Right lateral eye tubercle small, length Mitt. Mus. Nat.kd. Berl., Geowiss. Reihe 5 (2002) 101

9mm, and reniform. Lateral eye located antero- lacking proper resolution. The model presented laterally close to, but not touching, lateral mar- here builds on that of Plotnick & Baumiller gin of carapace. Median eyes or ocelli indistinct. (1988) and is based on apomorphic characters Prosomal appendages partly preserved. Chelicer- identified as part of a larger, ongoing phyloge- ae missing, but postcheliceral limbs robust and netic study of the entire Eurypterida by one of spinose. Limb VI modified into a paddle. Paddle us (OET). This work in progress aims to resolve unit forms an elongate oval, length 22 mm, width eurypterid relationships quantitatively through a 10 mm. Metastoma cardioid, length 16 111111, comprehensive parsimony analysis and the tree width 13 mm. Opisthosoma relatively broad, shown in Figure 6 should be taken as a prelimin- length 149 mm, maximum width 70 mm, without ary result of this project, albeit one for which we strong differentiation between pre- and postab- have good synapomorphies. domen. Posterior end of opisthosoma and telson Results and discussion: According to our absent. See also Stormer (1934) for further de- model (Fig. 6), derived in part from new infor- tails. mation regarding the position of the ocelli and shape of the metastoma in Grossopterus emer- ging from this study, we can now infer the posi- Affinities tion of G. overathi with respect to Slimonia and the hughmilleriids; the later represented here by Gross (1933) provisionally compared his new Nanahughmilleria Kjellesvig-Waering, 1961 and fossil to species of Eurypterus de Kay, 1825 and Para~ughmilleriaKjellesvig-Waering, 1961. Gros- Hughmilleria, ruling out the latter genus on stra- sopterus can provisionally be placed as sister tigraphical grounds since it was not known at group to (Slimonia + pterygotids), while, at least that time from the Devonian. Stormer (1934) based on the taxa studied here, Hughmilleriidae noted that the lateral position of the lateral eyes, may turn out to be a paraphyletic group. An i.e. close to the carapace margin, was more like Hughmilleria than Eurypterus. He further com- mented that the prosoma was reminiscent of some stylonurid eurypterids, although the Over- Acutimmus ath fossil can easily be excluded from this group since it has leg VI modified into a paddle TNncatiramus (Figs 1-2). Stormer (1934) also noted similarities 6 EiWOpteNS with Slirnonia in terms of the carapace shape and genital appendage, differentiating Grossop- Pteiygotus 5 terus from this genus by the detailed morphology of the latter structure (see diagnosis above). SZi- JaekefOptaNS I 4 monia also has a unique type of leg spinosity Siimonia (see e.g. Tollerton 1989) whereas that of Gros- 3 sopterus is more typical of eurypterids. Unfortu- Gmsoptenrs nately the absence of the telson makes it impos- 2 sible to resolve whether this structure in t Nanahughmilleria Grossopterus was lanceolate, like Hughmilleria I Parahughmilleria and most other eurypterids, or broad, which is very characteristic for Slimonia and the pterygo- Fig. 6. Provisional cladogram of selected taxa used to infer tids. the position of G. overathi and similar forms. The tree was constructed by hand based on characters identified as part of Phylogenetic position: A provisional phy- a larger (unpublished) analysis of eurypterid relationships (Tetlie in prep.). Suggested synapomorphies at the numbered logeny including G. overathi and representatives nodes are: [l]Eyes antelateral to ocelli, ocelli central (cf. of potentially related genera (see above) within Tollerton 1989, fig.7), eyes on anterior third; [2] Eyes on the Hughmilleriidae, Slimoniidae and Pterygotoi- lateral third, lateral sclerites absent on operculum; [3] 1st or- der differentiation of opisthosoma absent; [4] Eyes oval and dea was constructed to attempt to show the posi- marginal, appendage I1 non-spiniferous, 2nd order differen- tion of Grossopterus. The two previous unpub- tiation of opisthosoma absent; [S] Eye length >30% of proso- lished analyses (Plotnick 1983, Braddy 1996) are ma1 length, chelicerae enlarged with teeth, pretelson with dorsal keel and postlaterally expanded; [6] Genital appen- unsatisfactory due to the relatively small number dage type A undivided; [7] Largest principal tooth not per- of characters used, compared to the large num- pendicular to chelae, 1st principal tooth on free ramus great- ber of genera included, which resulted in trees er than that of the fixed ramus, keel of telson reduced. 102 Dunlop, J. et al., Redescription of Grossopterus evolutionary scenario is suggested here in which Eurypterids and fish relatively small-sized hughmilleriids with reni- form, intramarginal eyes, spiniferous walking Romer (1933) suggested that various Silurian legs and a lanceolate telson evolved towards the and Early Devonian jawless fish (e.g., Grossopterus condition with its slightly larger such as Heterostraci and ) evolved size and more anteriorly positioned eyes. This dermal armour specifically as a defence against trend is continued in Slimonia, i.e. even larger predation by eurypterids, and that the subse- size, marginal oval eyes, partial loss of spinifer- quent decline of eurypterids during the Devo- ous legs and development of a broader telson. nian was due to the increasing dominance of fas- The trend culminates in the pterygotids, reaching ter-swimming, jawed fish. In support of this up to a gigantic two metres in length. ChlupPc hypothesis, Romer (1933: 115) noted “Two ap- (1994) has estimated body lengths, excluding the parently unassociated facts . . .”. First, the diver- chelicerae, of 230-250 cm in the Czech species sity and size of the eurypterids appears to have bohemicus (Barrande, 1872). Other peaked around the late Silurian, coincidental pterygotid characters are development of the with the acme in the agnathans. Plotnick & Bau- chelicerae into massive, raptorial appendages, miller (1988: fig. 3) also demonstrated a sharp complete reduction of leg spination and huge, peak in pterygotid diversity at the end of the Si- anteriorly placed eyes, with the eye length being lurian. Second, the decline in the eurypterids about one third that of the prosoma. through the Devonian - they barely made it through to the - coincides with a rapid P t e r y g o ti d s : An interesting aspect of our increase in the numbers of jawed fish and a cor- model is that the pterygotids, which were par- responding loss of these fishes heavy dermal ar- tially unresolved in the analyses of Plotnick mour. Of the eurypterid genera recognised by (1983) and Plotnick & Baumiller (1988) show sy- Tollerton (1989: tab. 8) about three-quarters (47 napomorphies implying a slightly different topol- out of 62) occur within this late Silurian to Early ogy to that expressed in these papers. In an un- Devonian time bracket, whereas only about a published study, Rawlinson (2000) investigated quarter of the genera (16 from 62) are recorded the functional morphology of the chelicerae of from the mid Devonian through to the Permian. pterygotid eurypterids, identifying two main Some genera fall within both time brackets, but functional types: cutters and crushers based on given the questionable assignment of some mate- their relative mechanical advantages (see Selden rial to taxa (cf. Tollerton 1994) it would be un- 1984 for details). Cutters were characterised by a wise to analyse these data in detail without taxo- mechanical advantage of less than 0.1, the pre- nomic revisions concentrating on common sence of an enlarged principal tooth on the fixed genera reported as having long stratigraphic ramus, and the inclined orientation of the proxi- ranges. mal tooth on the free ramus. In a preliminary Additionally, eurypterids are commonly fossi- cladistic analysis based on data in Braddy (1996) lized in association with fish, especially in Silur- together with new cheliceral characters, Rawlin- ian and Devonian sediments such as the Gros- son (2000) suggested a general evolutionary sopterus type locality, the Wahnbach-Schichten trend from crushers to cutters of the form: (Jae- fish bed at Overath discussed by Gross (1933); kelopterus (Pterygotus (Erettopterus (Acutiramus see also above. Romer (1933) listed several well- Truncatiramus)))).Our results (Fig. 6) are de- + known localities such as the Shawangunk Grits, rived from more characters, but resemble the USA, the Baltic and Bertie waterlimes, and the tree of Rawlinson (2000) and suggest that the of Scotland where eurypter- cutting type of chelicerae is synapomorphic for ids are found associated with fish, apparently to Acutiramus and Truncatiramus while the very the exclusion of other potential predators on the broad telsons in Pterygotus and Acutiramus are vertebrate fauna. Recent descriptions of euryp- convergent; something also suggested by Plot- terids from the Midland Valley of Scotland nick’s (1983) study. However, we were unable at (Braddy 2000) and the Anderson River region this stage to identify reliable synapomorphies of (Braddy & Dunlop 2000) again high- which could resolve the relative position of lighted this frequent co-occurence of eurypterids Pterygotus and Erettopterus. and fish. Furthermore, in a detailed review of eurypterid palaeocommunities, Plotnick (1999) noted that in around one-third of the Silurian and Early Devonian eurypterid localities (where Mitt. Mus. Nat.kd. Berl., Geowiss. Reihe 5 (2002) 103 associations are known), eurypterids are asso- References ciated with fish; see Plotnick (1999, appendix 10a, localities 1, 17, 23, 28, 41, 45-47, 49-54, 57, Agassiz, L. 1844-1845. Monographie des poissons fossils du 59-61, 63, 64, 66, 68, 70-72, 79, 80b, 84, and Vieux Grks Rouge ou Systkme Devonian. 171 pp, folio, Jent & Gassmann, Neuchdtel. 91) for details. The question is whether these Barrande, J. 1872. SystCme silurien du centre de la Boheme. widely documented fossil associations are simply lCre partie. Recherches palContologiques. - Supplement fortuitous or whether they imply strong ecologi- au Vol. 1. , crustacis divers et poissons. . Beall, B. S. & Labandeira C. C. 1990. Macroevolutionary pat- cal interactions such as predation? terns of the Chelicerata and Tracheata. In Culver, s. J. Functional morphological studies of pterygotid (ed.) Arthropod Paleobiology, Short Courses in Palaeo- chelicerae suggest that they were designed for biology, NO.3: 257-284. The Paleontological Society. Braddy, S. J. 1996. Palaeobiology of the Eurypterida. - Un- the rapid capture of fast-moving prey (Selden published Ph.D. thesis, University of Manchester, 505 pp. 1984) and fish would be an obvious candidate. - 2000. Eurypterids from the Early Devonian of the Mid- Selden also noted how the saw-like teeth on the land Valley of Scotland. - Scottish Journal of Geology chelicerae of the pterygotid Acutiramus resemble 36 115-122. Braddy, S. J. & Dunlop, J. A. 1997. The functional morphol- fish-descaling implements and thus might have ogy of mating in the Silurian eurypterid, Baltoeurypterus been adapted specifically to deal with verte- tetrugonophthalmus (Fischer, 1839). - Zoological Journal brates. Rawlinson’s (2000) conclusions on an of the Linnean Society 121 435-461. - 2000. Early Devonian eurypterids from the Northwest evolutionary trend towards cutting pterygotid Territories of Arctic Canada. - Canadian Journal of chelicerae have also been noted above. Although Earth Sciences 37 1167-1175. no direct evidence (in the form of gut contents Burmeister, H. 1843. Die Organisation der Tnlobiten, aus ih- ren lebenden Verwandten entwickelt; nebst einer system- or disjecta) for eurypterids preying on fish is atischen Uebersicht aller zeither beschribenen Arten. 148 known, putative eurypterid coprolites from the pp., G. Reimer, Berlin. Hagshaw Hills of Scotland contain disarticulated ChlupiE, 1. 1994. Pterygotid eurypterids (Arthropoda, Cheli- cerata) in the Silurian and Devonian of Bohemia. - Jour- fish fragments (Selden 1984), supporting Ro- nal of the Czech Geological Society 39 (2-3): 147-162 mer’s general argument. Clarke, J. M. & Ruedemann, R. 1912. The Eurypterida of However, Romer’s proposal is not without its New York. - Memoirs of the State Museum of New critics. Recently, Gee (2000: 125) stated that this York 14: 1-439. de Kay, J. E. 1825. Observations of a fossil crustaceous ani- hypothesis “. . . paints a cartoon version of reality mal of the order . - Annals of the New . . . playing down complex ecological interrela- York Lyceum of Natural History 1: 375-377. tionships and ignoring other possibilities.” Gee Dunlop J. A. & Webster, M. 1999. Fossil evidence, terrestria- lization and phylogeny. - The Journal of Ara- (2000) favoured an alternative interpretation in chnology 27 86-93. which the dermal armour of Agnatha primarily Gee, H. 2000. Deep Time: Cladistics, the revolution in evolu- evolved as a phosphate store. Eurypterid-fish co- tion. 272 pp, Fourth Estate, London. Gross, W. 1933. Die unterdevonischen Fische und Gigantos- evolution is an attractive hypothesis with some traken von Overath. - Abhandlungen der PreuSischen circumstantial evidence in its favour, but which is Geologischen Landesanstalt (N. F.) 145: 41 -77. nevertheless difficult to prove quantitatively. In Kjellesvig-Waering, E. N. 1951. Downtownian (Silurian) Eur- ypterida from Perton, near Stoke Edith, Herefordshire. - our analysis, Grossopterus resolves as the sister Geological Magazine 88: 1-24. group of Slimonia plus the pterygotids and may - 1961. The Silurian Eurypterida of the Welsh Borderland. therefore be part of a basal lineage in this ulti- - Journal of Paleontology 35: 789-835. mately successful clade which exploited the niche - 1964. A synopsis of the family Clarke and Ruedemann, 1912 (Eurypterida). - Journal of Paleontol- of large size and, perhaps, vertebrate predation. ogy 38 331-361. - 1973. A new Silurian Slimoriia (Eurypterida) from Boli- via. - Journal of Paleontology 47: 549-550. Page, D. 1856. Advanced text-book of Geology. 326 pp., Wil- Acknowledgements liam Blackwood & Sons, Edinburgh. Plotnick, R. E. 1983. Patterns in the evolution of the euryp- We thank the Institut ftir Palaontologie of the MfN, Berlin terids. - Unpublished Ph.D. thesis, University of Chicago, for inviting this contribution, Dr. Christian Neumann (Ber- 411 pp. lin) for the loan of material in his care, Dr. Stefan Schultka - 1999. Habitat of Llandoverian- eurypterids. In (Berlin) for valuable advice on the Overath locality and Vera Boucot, A. & 5. Lawson (eds) Paleocommunities: A Case Heinrich (Berlin) for preparing the photographs. Drs Paul Study from the Silurian and Lower Devonian: 106-131. Selden (Manchester) and Carsten Brauckmann (Clausthal- Cambridge University Press. Zellerfeld) are thanked for suggesting improvements to the Plotnick, R. E. & Baumiller, T. K. 1988. The pterygotid tel- manuscript. OET acknowledges NFR grant 1456561432 into son as a biological rudder. - Lethaia 21 13-27. eurypterid phylogeny and evolution. Rawlinson, S. 2000. The functional morphology of raptorial appendages in predatory fossil arthropods. - Unpub- lished M.Sc. thesis, University of Bristol, 96 pp. Romer, A. S. 1933. Eurypterid influence on vertebrate his- tory. - Science 78: 114-117. 104 Dunlop, J. et al., Redescription of Grossopterus

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